Non-transparent microvoided axially stretched film, production process therefor and process for obtaining a transparent pattern therewith

ABSTRACT

A film consisting essentially of a continuous phase linear polyester matrix having dispersed therein a non-crosslinked random SAN-polymer and dispersed or dissolved therein at least one ingredient from the group of ingredients consisting of inorganic opacifying pigments, whitening agents, colorants, UV-absorbers, light stabilizers, antioxidants and flame retardants, wherein the film is white, microvoided, non-transparent and axially stretched; the linear polyester matrix has monomer units consisting essentially of at least one aromatic dicarboxylic acid, at least one aliphatic diol and optionally at least one aliphatic dicarboxylic acid; and the weight ratio of the linear polyester to the non-crosslinked SAN-polymer is in the range of 2.0:1 to 19.0:1, wherein one of the said at least one aliphatic dimethylene monomer units is selected from the group consisting of neopentylene and 1,4-cyclohexanedimethylene in a concentration of 30 mole % or less of all aliphatic dimethylene monomer units; the use of the film as or in synthetic paper; an image recording element comprising the film; a process for the preparing of the non-transparent microvoided axially stretched film; and a process for obtaining a transparent pattern therewith.

CROSS-REFERENCE TO RELATED PATENT APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/908,526 filed Mar. 28, 2007, U.S. Provisional Application No.60/908,536 filed Mar. 28, 2007, U.S. Provisional Application No.60/908,542 filed Mar. 28, 2007, U.S. Provisional Application No.60/908,545 filed Mar. 28, 2007, and U.S. Provisional Application No.60/975,300 filed Sep. 26, 2007, which are all incorporated by reference.In addition, this application claims the benefit of European ApplicationNo. 07104953.0 filed Mar. 28, 2008, European Application No. 07104947.2filed Mar. 28, 2007, European Application No. EP 07104948.0 filed Mar.28, 2007, European Application No. 07104950.6 filed Mar. 28, 2007, PCTApplication No. PCT/EP07/060,359 filed Oct. 1, 2007, PCT/EP07/060,218filed Sep. 26, 2007, PCT/EP07/060,380 filed Oct. 1, 2007 andPCT/EP07/060,373 filed Oct. 1, 2007, which are all also incorporated byreference.

FIELD OF THE INVENTION

The present invention concerns non-transparent microvoided axiallystretched films, a production process therefor and process for obtaininga transparent pattern therewith.

BACKGROUND OF THE INVENTION

U.S. Pat. No. 3,755,499 discloses a synthetic sheet for writing purposeswhich consists essentially of a linear polyester selected from the groupconsisting of polyethylene terephthalate, polyethylene isophthalate, andcopolymers of ethylene terephthalate and ethylene isophthalate, and ahigh polymer having a higher glass transition point than that of saidlinear polyester at a mixing ration of from 7 to 35% by weight of thelatter with respect to the polymer mixture, which high polymer isselected from the group consisting of a polymethylmethacrylate, acopolymer of acrylonitrile an styrene, a copolymer of acrylonitrile,butadiene and styrene, said synthetic sheet having a very finelycoarsened surface due to said high polymer which is uniformly dispersedin said linear polyester to constitute the nuclei for the irregularsurface thereof. Both simultaneous and sequential stretching of thesemixed polymer materials are disclosed usually at 85 to 95° C. withstretching ratios from 2 to 3.5 times the original length, the sheetbeing adjusted for writability and opacity in conformity with itseventual use. The object of the invention of U.S. Pat. No. 3,755,499 isstated to be the provision of a synthetic sheet for writing and similarother purposes having improved surface condition, opacity, and otherrequisite properties. U.S. Pat. No. 3,755,499 further discloses that thethermoplastic resin to be mixed may or may not have compatibility withthe linear polyester, provided that it can be substantially uniformlymixed with and dispersed in the linear polyester at the time of forming,that the formed film, regardless of whether it is transparent or not,may produce a uniform mat surface upon being stretched and the film thusobtained is heat-shrinkable, acceptable in its writing properties, andpossesses adequate opacity and that in order to further improvestability in the film size at a high temperature, it may be heat-treatedat a temperature above the stretching temperature of the linearpolyester and below the melting point of both mixing thermoplastic resinand the linear polyester. EXAMPLE 2 exemplifies the mixing of acopolymer of acrylonitrile and styrene having a glass transitiontemperature of 100 to 105° C. with polyethylene terephthalate inconcentrations of 7 and 35% by weight and the forming of 150 μm thickfilm samples by melt-extrusion through a T-die. These film sheets werethen stretched simultaneously by a biaxial stretching machine at astretch ratio twice as large as the original length of the film in thelongitudinal as well as transverse directions thereof at 85° C. and alsostretched simultaneously biaxially three times longitudinally and threetimes transversely at 85° C. The resulting films were reported to havethe following properties:

acrylonitrile-styrene copolymer (% by wt.) 7 7 35 35 Polyethyleneterephthalate (% by wt.) 93 93 65 65 stretch ratio (L × W) times 2 × 2 3× 3 2 × 2 3 × 3 thickness after stretching (μm) 48 26 45 25 rupturestrength (kg/cm) 880 1210 650 730 elongation at Breaking Point (%) 11045 55 23 light Transmission Factor (%) 80.8 84.2 72.3 77.6 haze value(%)92.5 90.6 94.3 96.6 writability [pencil hardness] ≦4H ≦3H ≦4H ≦3HU.S. Pat. No. 3,755,499 fails to disclose the influence of addition ofan inorganic opacifying pigment or of the image-wise heating on theopaque microvoided films disclosed therein.

U.S. Pat. No. 4,174,883 discloses a rear projection screen whichcomprises a light scattering member composed of a melted mixtureconsisting essentially of a dispersion medium polymer and a dispersedphase polymer dispersed therein, said melted mixture being obtained bymelting and then mixing said polymers, wherein the absolute value of thedifference between the refractive index of the dispersion medium polymerand the maximum refractive index of the dispersed phase polymer is from0.01 to 0.25, and wherein the dispersion medium polymer is a memberselected from high density polyethylene, low density polyethylene,polypropylene, 6,6-nylon, polyethylene terephthalate and polystyrene andthe dispersed phase polymer is at least one member selected from thegroup consisting of high density polyethylene, low density polyethylene,polypropylene, polyethylene terephthalate, 6-nylon, 6,6-nylon,6,10-nylon, polymethyl methacrylate, polymethyl acrylate, polyvinylchloride resins, polyvinyl acetate resins, polyacetal resins,polystyrene, polycarbonates, nitrile rubber, neoprene rubber,chloroprene rubber, styrene-butadiene rubber, ethylene-vinyl acetatecopolymers, and styrene acrylonitrile copolymers.

U.S. Pat. No. 4,128,689 discloses a process for preparing thermoplasticsheets or webs, which process comprises the steps of: (i) extruding afoamable thermoplastic polymer mixture through the die of a screwextruder to produce a foamed extrudate in sheet or web form, thefoamable thermoplastic polymer mixture containing at least a first and asecond thermoplastic polymer, the first thermoplastic polymer beingsubstantially crystalline and having a higher melting point than, andbeing substantially immiscible with, the second thermoplastic polymer,and the temperature of extrusion being equal to or greater than themelting point of the first thermoplastic polymer; (ii) stretching thefoamed extrudate from step (i) in the direction of extrusion as itleaves the die to rupture most of the cells of the foamed extrudate andto elongate the walls of the collapsed cells in the direction ofstretch; (iii) compressing the stretched extrudate from step (ii) whileit remains plastic; and (iv) cooling and foamed, stretched andcompressed extrudate from step (iii). Furthermore, U.S. Pat. No.4,128,689 discloses that the first thermoplastic polymer is preferablyselected from high density polyethylene, polypropylene, polybutene-1,poly 4-methylpentene-1, polyethylene terephthalate, nylon 6, nylon 66and nylon 11 and the second thermoplastic polymer is preferably anon-crystalline thermoplastic polymer preferably selected from celluloseacetate, cellulose propionate, cellulose acetate butyrate, ethylcellulose, polystyrene, styrene-acrylonitrile copolymers,polycarbonates, styrene and methyl styrene copolymers and phenyleneoxide polymers.

U.S. Pat. No. 4,243,769 discloses a method for providing a grosslyhomogeneous, permanently miscible mixture of polymers which hasproperties not evident in a simple blend of the polymers and which doesnot separate spontaneously into the component polymers, which comprisesuniformly mixing (a) a polymer component containing a nitrilefunctionality with (b) a polymer component containing hydroxyl oresterified hydroxyl functional groups condensable with nitriles, saidpolymer components (a) and (b) tending to spontaneously separate from asimple blend thereof, in the presence of from about 0.001 to 8 percentby weight of the mixture of polymers and acid of an acid compatibilizingagent and for a period sufficient to provide the aforesaid permanentlymiscible mixture of polymers which, at ambient temperature, is in theform of a solid. Furthermore, U.S. Pat. No. 4,243,769 discloses that thenitrile group material is preferably selected from the group consistingof polyacrylonitrile, polymethacrylonitrile,methacrylonitrile-acrylonitrile-vinyl acetate terpolymer,styrene-acrylonitrile copolymer, acrylonitrile-acrylic ester copolymer,acrylonitrile-butadiene-styrene terpolymer, acrylonitrile-styrene-alphamethyl styrene terpolymer, nitrile rubber, polycaprolactam-acrylonitrilegraft copolymer, polyethylene-acrylonitrile graft copolymer,polyethylene terephthalate-acrylonitrile graft copolymer,cyano-styrene-methylmethacrylate copolymer, acrylonitrile-methyl vinylether copolymer, methacrylonitrile-alpha methylstyrene copolymer,cyanoethylated cellulose, cyanoethylated polyvinyl alcohol,cyanoethylated polyamide, cyanoethylated polystyrene and cyano-ethylatedsilicone polymer; and the chemically condensable material is preferablyselected from the group consisting of polyvinyl alcohol, polyvinylbutyral containing unreacted alcohol groups, ethylene-vinyl acetate,saponified or partly saponified ethylene-vinyl acetate copolymers,ethylene-vinyl acetate-sulfur dioxide terpolymer, vinyl chloride-vinylacetate, nylon grafted with vinyl acetate, polytetrafluoroethylenegrafted with vinyl acetate, polyvinyl alcohol grafted withbutylmethacrylate, vinyl acetate-isobutyl vinyl ether copolymer,styrene-allyl alcohol copolymer polyethylene adipate, styrenatedpolyester of maleic and phthalic acids with ethylene and propyleneglycols, poly(ethylene terephthalate), cellulose, hydroxyethylmethacrylate copolymer, hydroxybutyl vinyl ether copolymer, hydroxyethylmethacrylamide copolymer, polyethylene glycol, hydroxyl terminatedpolystyrene, hydroxyl terminated polybutadiene, and hydroxyl terminatedpolyisoprene.

U.S. Pat. No. 4,342,846 discloses a blend comprising: (1) a polyesterresin formed by reaction of a dicarboxylic acid and a diol, preferablypoly(ethylene terephthalate); and (2) an impact resistant interpolymercomprising crosslinked (meth)acrylate, crosslinkedstyrene-acrylonitrile, and uncrosslinked styrene-acrylonitrile polymericcomponents.

EP 0 436 178A2 discloses a polymeric shaped article characterized inthat said article is comprised of a continuous oriented polymer matrixhaving dispersed therein microbeads of a cross-linked polymer which areat least partially bordered by void space, said microbeads being presentin an amount of 5-50% by weight based on the weight of said orientedpolymer, said void space occupying 2-60% by volume of said article. EP 0436 178A2 further discloses that said cross-linked polymer preferablycomprises polymerizable organic material which is a member selected fromthe group consisting of an alkenyl aromatic compound having the generalformula Ar—C(—R)═CH₂ wherein Ar represents an aromatic hydrocarbonradical, or an aromatic halohydracarbon radical of the benzene seriesand R is hydrogen or the methyl radical; acrylate-type monomersincluding monomers of the formula CH₂═C(—R′)—C(—OR)═O wherein R isselected from the group consisting of hydrogen and an alkyl radicalcontaining from about 1 to 12 carbon atoms and R′ is selected from thegroup consisting of hydrogen and methyl; copolymers of vinyl chlorideand vinylidene chloride, acrylonitrile and vinyl chloride, vinylbromide, vinyl esters having the formula CH₂═CH—O—C(—R)═O wherein R isan alkyl radical containing from 2 to 18 carbon atoms; acrylic acid,methacrylic acid, itaconic acid, citraconic acid, maleic acid, fumaricacid, oleic acid, vinylbenzoic acid; the synthetic polyester resinswhich are prepared by reacting terephthalic acid and dialkylterephthalics or ester-forming derivatives thereof, with a glycol of theseries HO(CH₂)_(n)OH, wherein n is a whole number within the range of2-10 and having reactive olefinic linkages within the polymer molecule,the hereinabove described polyesters which include copolymerized thereinup to 20 percent by weight of a second acid or ester thereof havingreactive olefinic unsaturation and mixtures thereof, and a cross-linkingagent selected from the group consisting of divinylbenzene, diethyleneglycol dimethacrylate, diallyl fumarate, diallyl phthalate and mixturesthereof.

EP-A 0 654 503 (which corresponds to U.S. Pat. No. 5,457,018) disclosesa shaped article prepared from a polymer blend of 50 to 97 wt. % of alinear polyester and 3 to 50 wt. % of a polymer containing styrene e.g.a graft polymer of acrylonitrile, butadiene and styrene (ABS), astyrene-acrylonitrile copolymer or a high impact polystyrene (HIPS),wherein the percentages relate to the sum of the polyester and thepolymer containing styrene. EP-A 0 654 503 further discloses that apreferred polyester contains at least 80 wt. % polyethyleneterephthalate and may contain up to 20 wt. % polyethylene isophthalateand the support material according to the invention may contain furtheradditives, for example pigments, in particular TiO₂, BaSO₄, CaCO₃,optical whiteners or blue dyes, which further increase covering powerand improve sharpness, in particular 0.5 to 10 wt. %, related to thetotal weight of the constituent used, preferably 2 to 10, preferably 3.5to 6.5 wt. % of TiO₂ pigment, preferably of the anatase type, are added.Example 3 discloses the blending of 15 wt % related to the whole weightof constituents used, of a copolymer prepared from 72 wt % of styreneand 28 wt % acrylonitrile with an M_(w) of approximately 115,000 andM_(w)/M_(n)≦3 then drying at 75° C. followed by melting in a PETextruder, extrusion through a slot, longitudinal stretching, applicationof a subbing layer, transverse stretching and heat-setting for 1 minuteat 160° C. No further ingredients are disclosed.

JP 09-255806A discloses a void-containing polyester film suitable foruse in recording paper containing a number of minute voids produced bymixing a polyester with a thermoplastic resin incompatible with thepolyester and orienting the obtained polymer mixture in at least onedirection with the thermoplastic resin incompatible with the polyesterbeing present in the film in the form of particles having a major axisdiameter of 1-50 μm, a thickness of ≦10 μm and a major axis/thicknessratio of 2-100. JP 09-255806A further discloses that the thermoplasticresin incompatible with the polyester may be polyethylene,polypropylene, polymethyl pentene and such polyolefin type resins,ionomer resin EP rubber and such copolymer polyolefin resins,polystyrene, styrene-acrylonitrile copolymers,styrene-butadiene-acrylonitrile copolymers and such polystyrene typeresins, polyacrylate resins, polycarbonate resins or polyacrylonitriletype resins. JP 09-255806A exemplifies opaque and translucent biaxiallystretched poly(ethylene terephthalate) using polystyrene orpoly(methylpentene) as the incompatible thermoplastic resin andpigmentation with titanium dioxide.

JP 2004-196951A discloses a polyester film, which is a film consistingof 78 to 55 weight % of a polyester (1) with butylene terephthalaterepeating units as main component and 22 to 45 weight % ofacrylonitrile-styrene copolymer (2), having as distinctive feature thatthe acrylonitrile-styrene copolymer (2) is dispersed in particle shapeinside the polyester (1), the average particle length in major axisdirection of those dispersed particles is 3 to 50 •m, the averageparticle length in minor axis direction is less than 5 •m, the averageaspect ratio is 2.0 or more, the film's tear strength in the directionorthogonal to the major axis direction of the dispersed particles (T(•))and the tear strength in the major axis direction (T(s)) are in arelation of T (•)/T(s)>1.0, and it has easy tear property in thedirection orthogonal to the major axis direction of the dispersedparticles. The concentration of acrylonitrie in the styrene-acrylonitriepolymer.

U.S. Pat. No. 6,703,193 discloses an image recording element comprisinga microvoided layer comprising a continuous phase polyester matrixhaving dispersed therein crosslinked organic microbeads andnon-crosslinked polymer particles that are immiscible with the polyestermatrix of said microvoided layer. U.S. Pat. No. 6,703,193 furtherdiscloses that if only non-crosslinked polymer particles that areimmiscible with the polyester matrix are used in the microvoided layerof a silver halide display media the raw material and manufacturing costis low, as a compounding step is not required, but the image sharpnessis very poor due to the relatively large voids that result. Thusalthough the use of immiscible polymer particles as voiding agents inimaging media is attractive from a cost standpoint, the quality withrespect to sharpness is prohibitively inferior. U.S. Pat. No. 6,703,193also discloses that it has been unexpectedly discovered that by mixingboth the crosslinked organic microbeads and the non-crosslinked polymerparticles that are immiscible with polyester into the polyester matrixof the microvoided layer the deficiencies of the void initiators whenused singularly are synergistically overcome, especially with respect toimage quality and manufacturability. The combination of crosslinkedorganic beads and non-crosslinked polymer particles immiscible in apolyester matrix enjoys the quality, with respect to sharpness ofmicrobead-voided media, without the expected degradation associated withthe addition of a material with poor sharpness quality, with significantcost reductions and manufacturing time and effort reductions resultingfrom the need to use less costly raw material which in turn lowers thetime and effort needed to compound microbeads with matrix polymer. U.S.Pat. No. 6,703,193 also discloses that the voided layer may containwhite pigments which are known to improve the photographic responsessuch as whiteness or sharpness such as titanium dioxide, barium sulfate,clay, calcium carbonate or silica; and that addenda may be added to thelayers to change the color of the imaging element. U.S. Pat. No.6,703,193 fails to disclose the influence of image-wise heating on theopaque microvoided films disclosed therein.

The prior art non-transparent microvoided axially stretched film hassuffered from insufficient opacity together with a lack of dimensionalstability or sufficient dimensional stability and insufficient opacity.Moreover, for particular applications the whiteness of thenon-transparent microvoided axially stretched film was insufficient.

ASPECTS OF THE INVENTION

It is therefore an aspect of the present invention to provide animproved non-transparent microvoided axially stretched film.

It is therefore a further aspect of the present invention to provide aprocess for producing an improved non-transparent microvoided axiallystretched film.

It is therefore also an aspect of the present invention to provide aprocess for obtaining a transparent pattern in a non-transparentmicrovoided axially stretched film.

Further aspects and advantages of the invention will become apparentfrom the description hereinafter.

SUMMARY OF THE INVENTION

It has been surprisingly found that addition of small quantities of anopacifying inorganic pigment enables the thermal fixation (setting)process necessary to realize acceptable dimensional stability to becarried out at lower temperatures, which surprisingly results in a lossin opacity during thermal fixation, which is substantially lower thanthat occurring at the higher thermal fixation temperatures, which wouldotherwise be necessary. It has also been surprisingly found that opacityis promoted by using lower temperatures than conventionally used duringstretching and in particular by using lower temperatures thanconventionally used with polyethylene terephthalate-SAN-polymer blendsduring transversal stretching and by adjusting the polyester matrixcomposition to make this realizable.

Aspects of the present invention are realized by a film consistingessentially of a continuous phase linear polyester matrix havingdispersed therein a non-crosslinked random SAN-polymer and dispersed ordissolved therein at least one ingredient from the group of ingredientsconsisting of inorganic opacifying pigments, whitening agents,colorants, UV-absorbers, light stabilizers, antioxidants and flameretardants, wherein the film is white, microvoided, non-transparent andaxially stretched; the linear polyester matrix has monomer unitsconsisting essentially of at least one aromatic dicarboxylate, at leastone aliphatic dimethylene and optionally at least one aliphaticdicarboxylate; the weight ratio of the linear polyester to thenon-crosslinked SAN-polymer is in the range of 2.0:1 to 19.0:1; and oneof the said at least one aliphatic dimethylene monomer units is selectedfrom the group consisting of neopentyl glycol and1,4-cyclohexanedimethanol in a concentration of 30 mole % or less of allaliphatic dimethylene monomer units.

Aspects of the present invention are also realized by the use of theabove-described non-transparent microvoided axially stretched film as orin synthetic paper.

Aspects of the present invention are also realized by an image recordingelement comprising the above-described non-transparent microvoidedaxially stretched film.

Aspects of the present invention are also realized by a process forpreparing a non-transparent microvoided axially stretched filmcomprising the steps of: i) mixing at least one linear polyester havingmonomer components selected from the group consisting of at least onearomatic dicarboxylic acid, at least one aliphatic diol and optionallyat least one aliphatic dicarboxylic acid, a non-crosslinked randomSAN-polymer and at least one ingredient from the group of ingredientsconsisting of inorganic opacifying pigments, whitening agents,colorants, UV-absorbers, light stabilizers, antioxidants and flameretardants in a kneader or an extruder to produce a mixture comprisingthe non-crosslinked random SAN-polymer in a polyester matrix, ii)forming the mixture produced in step i) in a thick film followed byquenching; and iii) stretching said thick film at a stretching tensionof >2.5 N/mm² at a temperature between the glass transition temperatureof said SAN-polymer and the glass transition temperature of said linearpolyester to at least twice the initial length, wherein the weight ratioof the polyester matrix to said non-crosslinked random SAN-polymer is inthe range of 2.0:1 to 19.0:1 and wherein one of the said at least onealiphatic dimethylene monomer units is selected from the groupconsisting of neopentylene and 1,4-cyclohexanedimethylene in aconcentration of 30 mole % or less of all aliphatic dimethylene monomerunits.

Aspects of the present invention are also realized by a process forobtaining a transparent pattern comprising the step of: image-wiseapplication of heat optionally supplemented by the application ofpressure to the above-described non-transparent microvoided axiallystretched film.

Preferred embodiments of the present invention are disclosed in thedetailed description of the invention.

DETAILED DESCRIPTION OF THE INVENTION Definitions

The term voids or microvoids, as used in disclosing the presentinvention, means microcells, minute closed cells, cavities, bubbles orpores or cellulation, which, for example, can be formed in an orientedpolymeric film during stretching as the result of a void-initiatingparticle initiated by particles that are immiscible with the polyestermatrix. The voids or microvoids can be unfilled or filled with air or avapour of some sort. Even if initially unfilled the voids or microvoidsmay over time become filled with air or a vapour of some sort.

The term “opaque”, means a percentage opacity to visible light ofgreater than 90% as determined according to ASTM D589-97 or according toopacity test T425m-60 as published by TAPPI, 360 Lexington Avenue, NewYork, USA.

The term foam, as used in disclosing the present invention, means asubstance that is formed by trapping many gas bubbles in a liquid orsolid.

The term film, as used in disclosing the present invention, is anextruded sheet of a particular composition or a sheet consisting of amultiplicity of films with the same or different compositions producedby co-extrusion of liquids with the same or different compositions incontact with one another. The term film is also applied to axially andbiaxially stretched films. The terms film and foil are usedinterchangeably in the present disclosure.

The term “non-photographic image”, as used in disclosing the presentinvention, means a image which is not produced with a conventionalsilver halide gelatinous emulsion.

The term dicarboxylate monomer unit in a linear polyester, as used indisclosing the present invention, means a monomer unit derived eitherfrom a dicarboxylic acid or an ester thereof.

The term dimethylene aliphatic monomer unit in a linear polyester, asused in disclosing the present invention, means a monomer unit derivedfrom a dimethylene aliphatic diol or an ether thereof, wherein the termaliphatic includes alicylic.

The term linear polyester, as used in disclosing the present invention,means a polyester comprising hydrocarbon dimethylene and dicarboxylatemonomer units.

The term linear aromatic polyester, as used in disclosing the presentinvention, means a polyester comprising aliphatic dimethylene andaromatic dicarboxylate monomer units.

The term inorganic opacifying pigment, as used in disclosing the presentapplication, means a pigment capable of opacifying (i.e. rendering moreopaque) which includes substantially white inorganic pigments having arefractive index of at least 1.4 and pigments, which as a dispersion ina polymer are capable upon stretching of causing opacity due tomicrovoiding.

The term whitening agent, as used in disclosing the present invention,means a white/colourless organic compound which exhibits a blueluminescence under the influence of ambient UV-light.

The term “support”, as used in disclosing the present invention, means a“self-supporting material” so as to distinguish it from a “layer” whichmay be coated as a solution or dispersion, evaporated or sputtered on asupport, but which itself is not self-supporting. It also includes anoptional conductive surface layer and any treatment necessary for, orlayer applied to aid, adhesion.

The term overprintable, as used in disclosing the present invention,means capable of being overprinted by conventional impact and/ornon-impact printing processes.

The term conventional printing processes, as used in disclosing thepresent invention, includes but is not restricted to ink-jet printing,intaglio printing, screen printing, flexographic printing, offsetprinting, stamp printing, gravure printing, dye transfer printing,thermal sublimation printing and thermal and laser-induced processes.

The term pattern, as used in disclosing the present invention, means anon-continuous layer which can be in any form of lines, squares, circlesor any random configuration.

The term layer, as used in disclosing the present invention, means a(continuous) coating covering the whole area of the entity referred toe.g. a support.

The term “non-transparent film”, as used in disclosing the presentinvention, means a film capable of providing sufficient contrast to atransparent image to make the image clearly perceptible. Anon-transparent film can be an “opaque film”, but need not necessarilybe completely opaque in that there is no residual translucence i.e. nolight penetration through the film. Optical density in transmission asmeasured with a MacBeth TR924 densitometer through a visible filter canprovide a measure of the non-transparency of a film. ISO 2471 concernsthe opacity of paper backing and is applicable when that property of apaper is involved that governs the extent to which one sheet visuallyobscures printed matter on underlying sheets of similar paper anddefines opacity as “the ratio, expressed as a percentage, of theluminous reflectance factor of a single sheet of the paper with a blackbacking to the intrinsic luminous reflectance factor of the same samplewith a white reflecting backing. 80 g/m² copy paper, for example, iswhite, non-transparent and has an optical density of 0.5 as measuredwith a MacBeth TR924 densitometer through a yellow filter according toISO 5-2 and metallized films typically have an optical density rangingfrom 2.0 to 3.0.

The term transparent, as used in disclosing the present invention, meanshaving the property of transmitting at least 50% of the incident visiblelight without diffusing it and preferably at least 70% of the incidentvisible light without diffusing it.

The term flexible, as used in disclosing the present invention, meanscapable of following the curvature of a curved object such as a drume.g. without being damaged.

The term “colorant”, as used in disclosing the present invention, meansdyes and pigments.

The term “dye”, as used in disclosing the present invention, means acolorant having a solubility of 10 mg/L or more in the medium in whichit is applied and under the ambient conditions pertaining.

The term “pigment” is defined in DIN 55943, herein incorporated byreference, as an inorganic or organic, chromatic or achromatic colouringagent that is practically insoluble in the dispersion medium under thepertaining ambient conditions, hence having a solubility of less than 10mg/L therein.

Non-Transparent Microvoided Axially Stretched Film

Aspects of the present invention are realized by a film consistingessentially of a continuous phase linear polyester matrix havingdispersed therein a non-crosslinked random SAN-polymer and dispersed ordissolved therein at least one ingredient from the group of ingredientsconsisting of inorganic opacifying pigments, whitening agents,colorants, UV-absorbers, light stabilizers, antioxidants and flameretardants, wherein the film is microvoided, non-transparent and axiallystretched; the linear polyester matrix has monomer units consistingessentially of at least one aromatic dicarboxylate, at least onealiphatic dimethylene and optionally at least one aliphaticdicarboxylate; and the weight ratio of the linear polyester to thenon-crosslinked SAN-polymer is in the range of 2.0:1 to 19.0:1, whereinone of the said at least one aliphatic dimethylene monomer units isselected from the group consisting of neopentylene and1,4-cyclohexanedimethylene in a concentration of 30 mole % or less ofall aliphatic dimethylene monomer units.

According to a first embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the non-transparent film is a white film.

According to a second embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the non-transparent film is a coloured film.

According to a third embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, at least one aliphatic dicarboxylate is present in thepolyester matrix in a concentration of less than 20 mole % of alldicarboxylate units in the linear polyester matrix.

According to a fourth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film is a biaxially stretched film.

According to a fifth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the weight ratio of the linear polyester to thenon-crosslinked SAN-polymer is in the range of 2.3:1 to 13:1, with arange of 2.5:1 to 10:1 being preferred, a range of 2.7:1 to 9.0:1 beingparticularly preferred and a range of 2.85:1 to 7.0:1 being especiallypreferred.

According to a sixth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the non-transparent microvoided axially stretchedself-supporting film is provided with at least one of alphanumericcharacters, an embossed pattern, an optionally embossed hologram and acontinuous, half-tone or digital image.

According to a seventh embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film is provided on at least one side with anoverprintable layer, i.e. suitable for impact or non-impact printing,which is preferably transparent. This transparent overprintable layercan be provided over at least one of alphanumeric characters, anembossed pattern, an optionally embossed hologram and a continuous,half-tone or digital image on a surface of the non-transparentmicrovoided axially stretched self-supporting film.

According to an eighth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film is provided on at least one side with atransparentizable porous overprintable layer i.e. suitable for impact ornon-impact printing e.g. ink-jet printing. Transparentizable porouslayers transparentized by the application of a liquid with anappropriate refractive index, which can also be applied image-wise, areas disclosed in EP-A 1 362 710 and EP-A 1 398 175. Thistransparentizable overprintable layer can be provided over at least oneof alphanumeric characters, an embossed pattern, an optionally embossedhologram and a continuous, half-tone or digital image on a surface ofthe non-transparent microvoided axially stretched self-supporting filmwith a transparent pattern.

Transparentization of part of the transparentizable porous receivinglayer can itself produce an image or the non-transparentized area of theopaque porous receiving layer can itself represent an image. Thetransparent pattern can, for example, be part of a banknote, a sharecertificate, a ticket, a credit card, an identity document or a labelfor luggage and packages.

According to a ninth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the non-transparent microvoided axially stretchedself-supporting film has a thickness in the range from about 15 μm toabout 500 μm, with from about 25 μm to about 300 μm being preferred.

According to a tenth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the non-transparent microvoided axially stretchedself-supporting film is provided with a subbing layer.

According to an eleventh embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film is exclusive of foam.

According to a twelfth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film is exclusive of foaming agent and/or decompositionproducts of a foaming agent.

According to a thirteenth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the non-transparent microvoided axially stretchedself-supporting film further contains an electroconductivity enhancingadditive e.g. a metallic salt which ionizes in the melt giving enhancedelectroconductivity such as magnesium acetate, manganese salts andcobalt sulphate. Suitable salt concentrations are about 3.5×10⁻⁴moles/mole polyester. Enhanced polyester melt viscosity enables improvedpinning of the melt on the chilling roller maintained at a temperatureof 5 to 25° C. (preferably 15 to 30° C.) to cool the extrudate therebyenabling higher stretching forces to be realized and hence enhancedvoid-forming and a higher degree of opacification.

Process for Producing a Non-Transparent Microvoided Axially StretchedFilm

Aspects of the present invention are also realized by a process forpreparing a non-transparent microvoided axially stretched filmcomprising the steps of: i) mixing at least one linear polyester havingmonomer components selected from the group consisting of at least onearomatic dicarboxylic acid and at least one aliphatic diol, anon-crosslinked random SAN-polymer and at least one ingredient from thegroup of ingredients consisting of inorganic opacifying pigments,whitening agents, colorants, UV-absorbers, light stabilizers,antioxidants and flame retardants in a kneader or an extruder to producea mixture comprising the non-crosslinked random SAN-polymer in apolyester matrix, ii) forming the mixture produced in step i) in a thickfilm followed by quenching e.g. to room temperature; and iii) stretchingsaid thick film at a stretching tension of >2.5 N/mm² at a temperaturebetween the glass transition temperature of said SAN-polymer and theglass transition temperature of said linear polyester to at least twicethe initial length, wherein the weight ratio of the polyester matrix tosaid non-crosslinked random SAN-polymer is in the range of 2.0:1 to19.0:1 and wherein one of the said at least one aliphatic dimethylenemonomer units is selected from the group consisting of neopentylene and1,4-cyclohexanedimethylene in a concentration of 30 mole % or less ofall aliphatic dimethylene monomer units.

According to a first embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the quenched extruded film has a thickness ofapproximately 10 μm to approximately 6000 μm, with a thickness ofapproximately 100 to approximately 5000 μm being preferred, a thicknessof approximately 200 μm to approximately 3000 μm being particularlypreferred and a thickness of approximately 500 μm to approximately 2000μm being especially preferred.

The non-transparent microvoided axially-stretched film is produced byorienting the thick film by stretching e.g. in the machine direction orin a direction perpendicular to the machine direction (the transversaldirection). Preferably the non-transparent microvoided axially-stretchedfilm is biaxially stretched. Biaxial stretching is realized by orientingthe film by first stretching in one direction (e.g. in the machinedirection=MD) and then stretching in a second direction [e.g.perpendicularly to the machine direction=TD (transversal direction)].This orients the polymer chains thereby increasing the density andcrystallinity. Longitudinal orientation in the direction of extrusioncan be carried out with the aid of two rolls running at different speedscorresponding to the desired stretching ratio by setting the surfacespeed 2 of the rotating rollers relative to the linear extrusion speedV1 so that the stretch ratio is V2/V1. The longitudinal stretching ratioshould be sufficient to create voids.

The longitudinal stretching operations known in the art to produceaxially and biaxially oriented polyester film may be used. For instance,the combined film layers are passed between a pair of infra red heaterswhich heats the layers to a temperature above the glass transitiontemperature of the polyester (about 80° C. for polyethyleneterephthalate) in the region where the stretching occurs. The stretchingtemperatures should be close to the glass transition temperature of thecontinuous phase polymer in order to improve opacity. Furthermore, thestretching temperatures should be below the glass transition temperatureof the PETSAN-polymer. In the case of polyethylene terephthalate, thelongitudinal stretching is generally carried out at from about 80 toabout 130° C. During longitudinal stretching opacity is realized as aresult of the voids produced in the film extending longitudinally fromeach particle of dispersed polymer.

Transverse stretching is carried out at an angle substantially 90° tothe direction of longitudinal stretching, with the angle being typicallybetween about 70° and 90°. For transverse orientation use is generallymade of an appropriate tenter frame, clamping both edges of the film andthen drawing toward the two sides by heating the combined layers withthe primer layer(s) thereon by, for example, passing through hot airheaters which heat the film above the glass transition temperature. Inthe case of polyethylene terephthalate, the transverse stretching iscarried out at from about 80 to about 170° C., preferably from about 90to about 150° C. The transverse stretching of the film causes the voidsto extend transversely.

According to a second embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the stretching of the thick film is performed at astretching tension >2.5 N/mm², with a stretching tension >5.0 N/mm²being preferred and a stretching tension >7.0 N/mm² being particularlypreferred. The stretching tension increases with decreasing stretchingtemperature.

According to a third embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the film is biaxially stretched.

According to a fourth embodiment of the process for producingnon-transparent microvoided axially stretched film, according to thepresent invention, the process comprises a further step, step (iv), inwhich the film is subjected to a further stretching process at an anglesubstantially 90° to the first stretching process to at least twice theinitial length at a stretching tension of >2.5 N/mm², with a stretchingtension of >4.0 N/mm² being preferred.

According to a fifth embodiment of the process for producingnon-transparent microvoided axially stretched film, according to thepresent invention, the process comprises a further step, step (iv), inwhich the film is subjected to a further stretching process at an anglesubstantially 90° to the first stretching process to at least twice theinitial length at a stretching tension of >2.5 and step iv) is performedat a temperature at or below 30° C. above the glass transitiontemperature of the linear polyester matrix, with a temperature at orbelow 20° C. above the glass transition temperature of the linearpolyester matrix being preferred and a temperature at or below 10° C.above the glass transition temperature of the linear polyester matrixbeing particularly preferred. The realizable stretching tensionincreases with decreasing stretching temperature.

According to a sixth embodiment of the process for producingnon-transparent microvoided axially stretched film, according to thepresent invention, steps iii) and iv) are performed simultaneously e.g.with an apparatus produced by Brückner.

According to a seventh embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the process further comprises, as a fifth step, athermal fixation step.

According to an eighth embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the stretching ratio for longitudinal stretching isbetween about 2 and about 6, with between about 2.5 and about 5 beingpreferred and between 3 and 4 being particularly preferred. The higherthe stretching ratio, the higher is the opacity.

According to a ninth embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the transverse stretching ratio is in the range offrom about 2 to about 6, with a range of 2.5 to about 5 being preferredand a range of from about 3 to about 4 being particularly preferred. Thehigher the stretching ratio, the higher is the opacity. Furthermore, thehigher in %/min the stretching rate, the higher the opacity.

According to a tenth embodiment of the process for producing anon-transparent microvoided axially stretched film, according to thepresent invention, the linear polyester does not have butyleneterephthalate as the main component.

The axially or biaxially stretched film is finally passed through asecond set of hot air heaters which blow hot air at a temperature ofbetween 160 and 240° C. onto the film layers to heat-set or thermofixthe film layers. The heat-set temperature must be sufficient to obtaincrystallization of the polyester but care must be taken not to overheatthe layers since the voids can collapse. On the other hand increasingthe heat-set temperature improves the dimensional stability of the film.An appropriate mix of properties can be obtained by varying the heat-settemperature. The preferred heat-set or thermofixation temperature in thecase of polyethylene terephthalate or polyethylene naphthalate is atleast 140° C. and preferably at least 1500 and particularly preferablyat least 175° C.

Before or after longitudinal stretching a first subbing layer, called aprimer layer, may be applied to the non-voided polyester layer by acoating means such as an air knife coating system. The first subbinglayer is for example formed from a (meth)acrylate copolymer, apoly(meth)acrylate, a polyurethane, a sulphonated polyester or achloride containing copolymer such as vinylidene chloride copolymer inlatex form having some hydrophilic functionality through the presence ofa copolymerized unsaturated carboxylic acid which is applied as anaqueous dispersion.

Optical Density of the Film Due to Microvoids

The optical density of the film measured in transmission with a visiblefilter due to microvoids is obtained by measuring the optical density ofthe film without void-producing ingredients as a function of filmthickness to provide comparative values. The optical density of a filmmeasured in transmission with a visible filter due to voids is thenobtained by biaxially stretching a composition to which has been addedthe void-inducing ingredient and subtracting the measured opticaldensity measured in transmission with a visible filter from the opticaldensity measured in transmission with a visible filter for the filmcomposition without void-inducing ingredient for the film thicknessexpected on the basis of the longitudinal and transverse drawing ratios.

Linear Polyester

According to a fourteenth embodiment of the non-transparent microvoidedaxially stretched film according to the present invention, the linearpolyester comprises at least one aromatic polyester resin e.g.poly(ethylene terephthalate) or a copolymer thereof. Upon heating, e.g.during mixing in an extruder, the different linear polyester resinspresent will undergo metathesis, condensing and decondensing so as toevolve upon sufficiently long heating into a single resin.

According to a fifteenth embodiment of the non-transparent microvoidedaxially stretched film according to the present invention, the linearpolyester comprises isophthalate monomer units in a concentration inrespect of the total concentration of dicarboxylate monomer units of atleast 1 mole %, with at least 3 mole % being preferred and at least 5mole % being particularly preferred.

According to a sixteenth embodiment of the non-transparent microvoidedaxially stretched film according to the present invention, the linearpolyester comprises isophthalate monomer units in a concentration inrespect of the total concentration of dicarboxylate monomer units of 20mole % or less, preferably 15 mole % or less and particularly preferably12 mole % or less.

According to a seventeenth embodiment of the non-transparent microvoidedaxially stretched film according to the present invention, the linearpolyester is a copolymer of polyethylene terephthalate.

According to an eighteenth embodiment of the non-transparent microvoidedaxially stretched film according to the present invention, the linearpolyester comprises polyethylene terephthalate and a copolymer ofethylene terephthalate and ethylene isophthalate.

Suitable polyesters include those produced from aromatic, aliphatic, orcyclo-aliphatic dicarboxylic acids or their esters, the dicarboxylategroup having 4-20 carbon atoms, and aliphatic (including alicyclic)glycols or ethers thereof, the aliphatic dimethylene groups having 2-24carbon atoms, and mixtures thereof. Examples of suitable aromaticdicarboxylates include terephthalate, isophthalate, phthalate,naphthalene dicarboxylates and sodiosulfoisophthalate. Examples ofsuitable aliphatic dicarboxylates include succinate, glutarate, adipate,azelaiate (from azelaic acid), sebacate, fumarate, maleiate (from maleicacid) and itaconate. Examples of suitable alicylic dicarboxylate are1,4-cyclohexane-dicarboxylate, 1,3-cyclohexane-dicarboxylate and1,3-cyclopentane-dicarboxylate. Examples of suitable aliphaticdimethylenes include ethylene, propylene, methylpropylene,tetramethylene, pentamethylene, hexamethylene, neopentylene[—CH₂C(CH₃)₂—CH₂], 1,4-cyclohexane-dimethylene,1,3-cyclohexane-dimethylene, 1,3-cyclopentane-dimethylene,norbornane-dimethylene, —CH₂CH₂ (OCH₂CH₂)_(n)—, where n is an integerwith 1 to 5 being preferred, and mixtures thereof.

Such polyesters are well known in the art and may be produced bywell-known techniques, for example, those described in U.S. Pat. No.2,465,319 and U.S. Pat. No. 2,901,466.

According to a nineteenth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the linear polyester is a polymer having aromaticdicarboxylic acids selected from the group consisting of terephthalicacid, isophthalic acid and naphthalene dicarboxylic acid.

According to a twentieth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the linear polyester is a polymer having aliphatic diolsselected from the group consisting of ethylene glycol, diethyleneglycol, 1,4-butanediol, neopentyl glycol, 2-endo, 3-endo norbornanedimethanol and 1,4-cyclohexanedimethanol, with a combination of ethyleneglycol and 1,4-cyclohexanedimethanol being preferred.

According to a twenty-first embodiment of the non-transparentmicrovoided axially stretched film, according to the present invention,the linear polyester comprises polyethylene terephthalate and acopolymer of ethylene terephthalate and 1,4-cyclohexylene dimethyleneterephthalate.

According to a twenty-second embodiment of the non-transparentmicrovoided axially stretched film, according to the present invention,at least 1 mole % of the aliphatic dimethylene monomer units in thelinear polyester are neopentylene or 1,4-cyclohexanedimethylene monomerunits, with at least 3 mole % being preferred and at least 5 mole %being particularly preferred.

According to a twenty-third embodiment of the non-transparentmicrovoided axially stretched film, according to the present invention,20 mole % or less of the aliphatic dimethylene monomer units in thelinear polyester are neopentylene or 1,4-cyclohexanedimethylene monomerunits, with 18 mole % or less being preferred, 15 mole % or less beingparticularly preferred.

According to a twenty-fourth embodiment of the non-transparentmicrovoided axially stretched film according to the present invention,the number average molecular weight of the linear polyester is 10,000 to30,000.

Poly(ethylene terephthalate modified by small amounts of other monomersis especially preferred. Other suitable polyesters include liquidcrystal copolyesters formed by the inclusion of a suitable amount of aco-acid component such as stilbene dicarboxylic acid. Examples of suchliquid crystal copolyesters are those disclosed in U.S. Pat. No.4,420,607, U.S. Pat. No. 4,459,402 and U.S. Pat. No. 4,468,510.

According to a twenty-fifth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the linear polyester has a glass transitiontemperature from 40 to 150° C., preferably from 50 to 120° C. andparticularly preferably from 60 to 100° C.

According to a twenty-sixth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the linear polyester is orientable.

According to a twenty-seventh embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the linear polyester has an inherent viscositydetermined in a 0.5 g/dL solution of 60 wt % phenol and 40 wt %ortho-dichlorobenzene at 25° C. of at least 0.45 dl/g with an inherentviscosity of 0.48 to 0.9 dl/g being preferred and an inherent viscosityof 0.5 to 0.85 dl/g being particularly preferred and an inherentviscosity of 0.55 to 0.8 dl/g being especially preferred.

According to a twenty-eighth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the linear polyester does not have butyleneterephthalate as the main component.

Mixtures of polyesters undergo metathesis during mixing in the meltresulting in a copolymer being formed with the overall composition ofthe mixture. Examples of a suitable matrix include a blend comprisingpoly(ethylene terephthalate) and poly(1,4-cyclohexylene dimethyleneterephthalate).

Random SAN-Polymer

According to a twenty-ninth embodiment of the non-transparentmicrovoided axially stretched film according to the present invention,the concentration of SAN-polymer is at least 5% by weight, with at least10% by weight being preferred and at least 15% by weight beingparticularly preferred.

According to a thirtieth embodiment of the non-transparent microvoidedaxially stretched film according to the present invention, theconcentration of SAN-polymer is 35% by weight or less, with 30% or lessbeing preferred and 25% by weight or less being particularly preferred.

According to a thirty-first embodiment of the non-transparentmicrovoided axially stretched film according to the present invention,the concentration of AN-monomer units in the SAN-polymer is 15 to 35% byweight, with 18 to 32% by weight being preferred and 21 to 30% by weightbeing particularly preferred.

The SAN polymer additive of the present composition is a known genus ofpolymer consisting essentially of a styrenic monomer component,including styrene as well as an alpha-lower alkyl-substituted styrene ormixtures thereof and an acrylonitrilic monomer component includingacrylonitrile as well as an alpha-lower alkyl substituted acrylonitrileor mixtures thereof. By lower-alkyl is meant a straight or branchedchain alkyl group of 1 to 4 carbon atoms exemplified by the methyl,ethyl, isopropyl and t-butyl groups. In readily available SAN polymers,the styrene component is generally styrene, alpha-straight chain alkylsubstituted styrene, typically alpha-methyl-styrene, or mixtures thereofwith styrene being preferred. Similarly in the readily available SANpolymers, the acrylonitrile component is generally acrylonitrile,alpha-methyl-acrylonitrile or mixtures thereof with acrylonitrile beingpreferred.

In the SAN polymer the styrene component is present in a major weightproportion, i.e. in a weight proportion of greater than 50%, typicallyabout 65% to about 90%, especially about 70% to about 80%, based on thecombined weight of the styrene component and the acrylonitrilecomponent. The acrylonitrile component is present in a minor proportion,i.e. in a weight proportion of less than 50%, typically about 10% toabout 35% especially about 20% to 30% based on the combined weight ofthe styrene monomer component and the acrylonitrile monomer component.

The SAN polymer class is more particularly identified and described inR. E. Gallagher, U.S. Pat. No. 3,988,393, issued Oct. 26, 1976(especially at Column 9, lines 14-16 and in claim 8), in “Whittington'sDictionary of Plastics”, Technomic Publishing Co., First Edition, 1968,page 231, under the section headed “Styrene-Acrylonitrile Copolymers(SAN)”, and R. B. Seymour, “Introduction to Polymer Chemistry”,McGraw-Hill, Inc., 1971, page 200, (last two lines) to page 201 (firstline). The preparation of a SAN polymer by copolymerization of styreneand acrylonitrile is more particularly described in the “Encyclopedia ofPolymer Science and Technology”, John Wiley and Sons, Inc., Vol. 1,1964, pages 425-435.

According to a thirty-second embodiment of the non-transparentmicrovoided axially stretched film, according to the present invention,the number average molecular weight of the non-crosslinked randomSAN-polymer is 30,000 to 100,000, with 32,000 to 80,000 being preferred,35,000 to 70,000 being particularly preferred and 40,000 to 60,000 beingespecially preferred. Typical SAN-polymers have number averagedmolecular weights of 45,000 to 60,000 and polymer dispersities(M_(w)/M_(n)) of 1.2 to 2.5.

According to a thirty-third embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the weight average molecular weight of thenon-crosslinked random SAN-polymer is in the range of 50,000 to 200,000,preferably in the range of 75,000 to 150,000.

According to a thirty-fourth embodiment of the non-transparentmicrovoided axially stretched film, according to the present invention,the dispersed SAN-polymer has a number averaged particle size of 10 μmor less, with a number averaged particle size of 5 μm or less beingpreferred, a number averaged particle size of 2.5 μm or less beingparticular preferred and a number averaged particle size of 1.5 μm orless being especially preferred. The smaller the particle size of thedispersed SAN-polymer, the higher the opacity.

Inorganic Opacifying Pigment

According to a thirty-fifth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the concentration of inorganic opacifying pigment is≧0.1% by weight, with ≧1% by weight being preferred.

According to a thirty-sixth embodiment of the non-transparentmicrovoided axially stretched film of the present invention, theinorganic opacifying pigment is present in a concentration of ≦10% byweight, with ≦3% by weight being preferred.

According to a thirty-seventh embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film comprises ≦10% by weight of inorganicopacifying pigment each with a refractive index of less than 2.0, with≦3% by weight being preferred.

According to a thirty-eighth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film comprises ≦10% by weight of inorganicopacifying pigment each with a refractive index of at least 1.5.

According to a thirty-ninth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film further comprises an inorganic opacifyingpigment having a number averaged particle size between 0.1 and 10 μm,with 0.2 to 2 μm being preferred and 0.2 to 1 μm being particularlypreferred.

According to a fortieth embodiment of the transparent pattern in anon-transparent microvoided axially stretched self-supporting film,according to the present invention, the film further comprises aninorganic opacifying pigment selected from the group consisting ofsilica, zinc oxide, zinc sulphide, lithopone, barium sulphate, calciumcarbonate, titanium dioxide, aluminium phosphate and clays.

The titanium dioxide may have an anatase or rutile morphology and may bestabilized by alumina oxide and/or silicon dioxide. The aluminiumphosphate can be an amorphous hollow pigment e.g. the Biphor™ pigmentsfrom BUNGE.

The refractive indices of these pigments is given in the table below:

refractive index for inorganic opacifying pigment sodium line at 589.3nm kaolinite 1.53-1.57 bentonite 1.557 china clay 1.56 silica - silicagel 1.55 silica - cristobalite 1.487, 1.484 silica - quartz 1.544, 1.553calcium carbonate 1.59, 1.6, 1.58 calcium carbonate - calcite 1.486,1.64-1.66 barium sulphate - baryte 1.637, 1.638, 1.649, 1.64 Lithopone30% (zinc sulphide/barium sulphate) 1.84 zinc oxide (ultrafine) 1.9 zincoxide (zincite) 2.008, 2.029 zinc sulphide 2.37 titanium dioxide -anatase 2.554, 2.493, 2.55 titanium dioxide - rutile 2.616, 2.903, 2.76

Addition of an inorganic opacifying pigment has the advantage ofstabilizing the orientation of the polyester, so that thenon-transparent microvoided axially stretched self-supporting film canbe stabilized at temperatures of 175° C. without substantially affectingthe opacity of the non-transparent microvoided axially stretchedself-supporting film. Without the presence of an inorganic opacifyingpigment, such as BaSO₄ or TiO₂, thermofixing of the polyester ispossible, but only at the expense of some of the opacity of thenon-transparent microvoided axially stretched self-supporting film.Moreover, pigments with a refractive index below 2.0, such as BaSO₄, donot of themselves provide substantial opacity due to the smallrefractive index differences between the pigment and the polymer matrix.

Titanium dioxide particles dispersed in polymer films have of themselvesbeen found not to induce microvoiding upon stretched the films.

Whitening Agent

According to a forty-first embodiment of the non-transparent microvoidedaxially stretched film, according to the present invention, theconcentration of whitening agent is ≦0.5% by weight, with ≦0.1% byweight being preferred, ≦0.05% by weight being particularly preferred,≦0.035% by weight being especially preferred.

According to a forty-second embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film further comprises a whitening agent selectedfrom the group consisting of bis-benzoxazoles e.g.bis-benzoxazolyl-stilbenes and bis-benzoxazolyl-thiophenes;benzotriazole-phenylcoumarins; naphthotriazole-phenylcoumarins;triazine-phenylcoumarins and bis(styryl)biphenyls.

Suitable whitening agents are:

Manufacturer UVITEX ® OB CIBA UVITEX ® OB-ONE CIBA Eastobrite OB2,5-thiophenediylbis(5-tert- Eastman Chemical butyl-1,3-benzoxazole)bis-benzoxazolyl-stilbene bis-benzoxazolyl-thiophene

Flame Retardant

According to a forty-third embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film further comprises a flame retardant.

According to a forty-fourth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film further comprises a flame retardant selectedfrom the group consisting of: brominated compounds; organophosphoruscompounds; melamine; melamine-derivatives, e.g. melamine salts withorganic or inorganic acids such as boric acid, cyanuric acid, phosphoricacid or pyro/poly-phosphoric acid, and melamine homologues such asmelam, melem and melon; metal hydroxides e,g. aluminium hydroxide andmagnesium hydroxide; ammonium polyphosphates and zinc borate e.g. with acomposition of xZnO.yB₂O₃.zH₂O such as 2ZnO.3B₂O₃.3.5H₂O.

Suitable flame retardants include:

Manufacturer SAYTEX ® HP-7010 P/G brominated polystyrene AlbemarleCorporation SAYTEX ® HP-3010 brominated polystyrene AlbemarleCorporation SAYTEX ® 8010 ethane-1,2-bis(pentabromo- AlbemarleCorporation phenyl) SAYTEX ® BT-93 ethylene bis-tetrabromo- AlbemarleCorporation phthalimide SAYTEX ® BT-93W Ethylene bis-tetrabromo-Albemarle Corporation phthalimide SAYTEX ® CP-2000 brominated compoundAlbemarle Corporation SAYTEX ® 120 tetradecabromo-diphenoxy benzeneAlbemarle Corporation SAYTEX ® 102E Decabromodiphenyl oxide AlbemarleCorporation SAYTEX ® 9006L brominated compound Albemarle CorporationSAYTEX ® HP-900 brominated compound Albemarle Corporation SAYTEX ®HP-800A brominated compound Albemarle Corporation SAYTEX ® HP-800AGbrominated compound Albemarle Corporation SAYTEX ® BC70HS brominatedcompound Albemarle Corporation NcendX P-30 organophosphorus compoundAlbemarle Corporation MARTINAL ® OL-104 aluminium hydroxide AlbemarleCorporation MARTINAL ® OL-104/LE aluminium hydroxide AlbemarleCorporation MARTINAL ® OL-104/WE aluminium hydroxide AlbemarleCorporation MARTINAL ® OL-104/LFF aluminium hydroxide AlbemarleCorporation MARTINAL ® OL-104/LCD aluminium hydroxide AlbemarleCorporation MARTINAL ® OL-107 aluminium hydroxide Albemarle CorporationMARTINAL ® OL-107/LE aluminium hydroxide Albemarle CorporationMARTINAL ® OL-107/LFF aluminium hydroxide Albemarle CorporationMARTINAL ® OL-107/LCD aluminium hydroxide Albemarle CorporationMARTINAL ® OL/Q-107 aluminium hydroxide Albemarle Corporation MARTINAL ®OL-111/LE aluminium hydroxide Albemarle Corporation MAGNIFIN ® H3magnesium hydroxide Albemarle Corporation MAGNIFIN ® H5 magnesiumhydroxide Albemarle Corporation MAGNIFIN ® H7 magnesium hydroxideAlbemarle Corporation MAGNIFIN ® H10 magnesium hydroxide AlbemarleCorporation MAGNIFIN ® T2C magnesium hydroxide Albemarle CorporationMAGNIFIN ® T3C magnesium hydroxide Albemarle Corporation MELAPUR ® MCXLmelamine cyanurate CIBA MELAPUR ® MC50 melamine cyanurate CIBA MELAPUR ®MC25 melamine cyanurate CIBA MELAPUR ® 200 70 melamine polyphosphateCIBA MELAPUR ® MP melamine phosphate CIBA FIREBRAKE ® ZB a zinc boratecompound LUZENAC FIREMASTER ® PBS-64 brominated styrene-based GREATLAKES CHEMICAL technology CORP. FIREMASTER ® PBS-64HW brominatedstyrene-based GREAT LAKES CHEMICAL technology CORP. FIREMASTER ® CP-44Bcopolymer of brominated styrene GREAT LAKES CHEMICAL & glycidylmethacrylate CORP.

Antioxidant

According to a forty-fifth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film further comprises an antioxidant.

According to a forty-sixth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film further comprises an antioxidant selected for thegroup consisting of organotin derivatives, sterically hindered phenols,sterically hindered phenol derivatives and phosphites.

Suitable flame retardants include:

Manufacturer ETHANOX ® 310 Organotin catalyzed penta-erythritolAlbemarle Corporation tetrakis (3-(3,5-di-t-butyl-4-hydroxyphenyl)-propionate) ETHANOX ® 310TF “Tin-free” pentaerythritoltetrakis Albemarle Corporation (3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate) ETHANOX ® 314 1,3,5-tris(3,5-di-tert-butyl-4-Albemarle Corporation hydroxybenzyl)-1,3,5-tria-zine-2,4,6(1h,3h,5h)-trione ETHANOX ® 60 1,3,5-trimethyl-2,4,6-tris (3,5-di-Albemarle Corporation tert-butyl-4-hydroxy-benzyl) benzene ETHANOX ® 376octadecyl-3-(3,5-di-t-butyl-4- Albemarle Corporationhydroxyphenyl)-propionate ETHAPHOS ™ 368 tris-(2,4-di-t-butylphenyl)phosphite Albemarle Corporation ETHAPHOS ™ 326 Bis(2,4-di-t-butylphenyl) Albemarle Corporation pentaerythritol diphosphiteIRGANOX ® 259 CIBA IRGANOX ® 1010 CIBA IRGANOX ® 1425 CIBA IRGANOX ® B900 CIBA HOSTANOX ® O 3 Bis[3,3′-bis-(4′-hydroxy-3′-tert- CLARIANTbutyl-phenyl)butanoic acid]glycol ester HOSTANOX ® O 10tetrakis[methylene(3,5-di-t-butyl-4- CLARIANThydroxy-benzyl)isocyanurate HOSTANOX ® O 1/1 mixture of HOSTANOX ® O 10& CLARIANT 310 HOSTANOX ® O 3 HOSTANOX ® 245 ethylenebis(oxyethylene)bis-[3-(5-t- CLARIANTbutyl-4-hydroxy-m-tolyl)-propionate]

Light Stabilizers

According to a forty-seventh embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film further comprises a light stabilizer.

According to a forty-eighth embodiment of the non-transparentmicrovoided axially stretched self-supporting film, according to thepresent invention, the film further comprises a hindered amine lightstabilizer.

Suitable light stabilizers include:

Manufacturer LS-01 CHIMASSORB 119 CIBA LS-02 CHIMASSORB 944 CIBA LS-03TINUVIN ® 123 CIBA LS-04 TINUVIN ® 144 CIBA LS-05 TINUVIN ® 622 CIBALS-06 TINUVIN ® 765 CIBA LS-07 TINUVIN ® 770 CIBA LS-08 TINUVIN ® 783CIBA LS-09 TINUVIN ® 791 CIBA LS-10 TINUVIN ® B 75 CIBA LS-11 TINUVIN ®B 241 CIBA

UV-Absorbers

According to a forty-ninth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film further comprises a UV-absorber.

According to a fiftieth embodiment of the non-transparent microvoidedaxially stretched self-supporting film, according to the presentinvention, the film further comprises an UV-absorber selected from thegroup consisting of benzotriazole derivatives and triazine derivatives.

Suitable UV-absorbers include:

Manufacturer UV-01 CHIMASSORB CIBA UV-02 TINUVIN ® 213 CIBA UV-03TINUVIN ® 234 CIBA UV-04 TINUVIN ® 327 CIBA UV-05 TINUVIN ® 360 CIBAUV-06 TINUVIN ® 1577 CIBA UV-07 HOSTAVIN ® PR-25 propanedioic acid,[(4-methoxy- CLARIANT phenyl)-methylene]-, dimethyl ester UV-08SANDUVOR ® VSU 2-ethyl-2′-ethoxy-oxalanilide CLARIANT UV-09 HOSTAVIN ®B-CAP tetra-ethyl-2,2′-(1,4-phenylene- CLARIANTdimethylidene)-bismalonate UV-10 HOSTAVIN ® ARO 82-hydroxy-4-n-octyloxybenzophenone CLARIANT

Image Recording Element

Aspects of the present invention are also realized by an image recordingelement comprising the non-transparent microvoided axially stretchedfilm, according to the present invention.

According to a first embodiment of the image recording element,according to the present invention, the image is a non-photographicimage.

According to a second embodiment of the image recording element,according to the present invention, the film is provided on at least oneside with a transparent overprintable layer i.e. for impact andnon-impact printing.

According to a third embodiment of the image recording element,according to the present invention, the film is provided on at least oneside with a non-transparent overprintable layer i.e. suitable for atleast one impact and non-impact print technique.

According to a fourth embodiment of the image recording element,according to the present invention, the film is provided on at least oneside with a non-transparent transparentizable overprintable layer i.e.i.e. suitable for at least one impact and non-impact print technique.

According to a fifth embodiment of the image recording element,according to the present invention, the film is provided on at least oneside with an ink-jet receiving layer. Typical receiving layers areeither porous in the case of aqueous or solvent inks or pastes to enablerapid drying to the touch or are non-porous in the case of phase-changeinks or curable inks e.g. radiation curable inks. Porous receivinglayers typically comprise at least one pigment such as silica oralumina; at least one binder, such as an ammonium salt of astyrene-acrylate-acrylic acid terpolymer; a surfactant e.g. an anionicsurfactant such as an aliphatic sulphonate; optionally a levellingagent, such as polydimethylsiloxane, and optionally a mordant.

According to a sixth embodiment of the image recording element,according to the present invention, the film is provided on at least oneside with an imaging layer e.g. a photographic layer e.g. a silverhalide emulsion layer; a photothermographic element and a substantiallylight-insensitive thermographic element; and the dye receiver layer of adye thermal transfer system.

According to a seventh embodiment of the image recording element,according to the present invention, the film is provided on at least oneside with a writable layer e.g. with a pencil, ball-point pen andfountain pen.

Process for Obtaining a Transparent Pattern

Aspects of the present invention have been realized by a process forobtaining a transparent pattern comprising the step of: image-wiseapplication of heat optionally supplemented by the application ofpressure to a non-transparent microvoided axially stretched filmconsisting essentially of a continuous phase linear polyester matrixhaving dispersed therein a non-crosslinked random SAN-polymer and atleast one ingredient from the group of ingredients consisting ofinorganic opacifying pigments, whitening agents, colorants,UV-absorbers, light stabilizers, antioxidants and flame retardants,wherein the linear polyester has monomer components consistingessentially of at least one aromatic dicarboxylic acid, at least onealiphatic diol and optionally at least one aliphatic dicarboxylic acid,the weight ratio of the non-crosslinked SAN-polymer to the linearpolyester is in the range 3.0 to 9.0 and wherein the concentration ofAN-monomer units in the SAN-polymer is 18 to 35% by weight, with a theweight ratio of non-crosslinked SAN-polymer to the linear polyester isin the range 3.0 to 5.5 being preferred.

According to a first embodiment of the process for obtaining atransparent pattern, according to the present invention, the film is abiaxially stretched film.

According to a second embodiment of the process for obtaining atransparent pattern, according to the present invention, theconcentration of inorganic opacifying pigment is ≧0.1% by weight,preferably ≧1% by weight.

According to a third embodiment of the process for obtaining atransparent pattern, according to the present invention, theconcentration of whitening agent is ≦0.5% by weight, with ≦0.1% byweight being preferred, ≦0.05% by weight being particularly preferred,≦0.035% by weight being especially preferred.

According to a fourth embodiment of the process for obtaining atransparent pattern, according to the present invention, the heat isapplied by a heated or hot stamp, a thermal head, a heated or hot bar ora laser. The heating can be carried out from one or both sides of thefilm. The proportionate transparentization realized upon obtaining atransparent pattern, according to the present invention, increases withdecreasing film thickness, with thicknesses of 100 μm or less beingpreferred. Optical density changes of at least 0.4 can be readilyrealized or up to 40% without significant changes in film thickness.Moreover, the transparentization effect realized by the process forobtaining a transparent pattern, according to the present invention,results from a combination of heat supplied by a heat source, thepressure between the heat source and the film and the time the heatsource is applied. The heat has to be applied for at least 1 ms eithercontinuously or non-continuously. Heating with a thermal head can bewith a single heat pulse, but multiple short heating pulses arepreferred to avoid overheating of the heating elements. When a thermalhead is used a foil can be used between the thermal head and thenon-transparent microvoided axially stretched self-supporting filmduring the heating process e.g. a 6 μm thick PET-film can be interposedbetween the non-transparent microvoided film and the thermal head toprevent possible contamination of the thermal head. Thermal headprinters, such as the DRYSTAR-printers supplied by AGFA-GEVAERT N.V.,can be used produce the transparent pattern of the present inventione.g. as personalized watermarks.

This transparentization effect is accompanied by a relief pattern, whichcan be detected by touch i.e. in a tactile manner, and by changes inglossiness. This relief pattern is more pronounced the higher thetemperature of the heat source, this embossing effect increasing withtemperature between 110° C. and the melting point of the linearpolyester matrix. The tactile relief obtained by applying a hot stamp toa non-transparent microvoided axially stretched self-supporting film ismuch more pronounced than that obtained using a thermal head.

The degree of transparency realized depends upon the stamp/thermal headprinting conditions: time, temperature and pressure. The thermofixationhistory of the material is also important. The heated-inducedtransparentization of the non-transparent microvoided axially stretchedself-supporting film can be carried out before or after the optionalapplication of a layer, such as an ink-jet receiving layer and before orafter transparentization. The relative positioning of thetransparentized areas and transparency in the support can be of value asan additional security measure.

According to a fifth embodiment of the process for obtaining atransparent pattern, according to the present invention, the heat isapplied non-continuously.

According to a sixth embodiment of the process for obtaining atransparent pattern, according to the present invention, a transparentoverprintable layer is provided on the film prior to the image-wiseapplication of heat.

According to a seventh embodiment of the process for obtaining atransparent pattern, according to the present invention, a transparentoverprintable layer is provided on the film after the image-wiseapplication of heat.

INDUSTRIAL APPLICATION

Non-transparent microvoided axially stretched films, according to thepresent invention, can be used as synthetic paper for printing and otherapplications, as a support for non-photographic imaging materials e.g.impact and non-impact (e.g. electrophotography, electrography and inkjet) receiving materials, photothermographic recording materials,substantially light-insensitive thermographic recording materials, dyesublimation printing, thermal transfer printing, etc., in security andanti-counterfeiting applications e.g. in tickets, labels, tags, anID-card, a bank card, a legal document, banknotes and packaging and canalso be integrated into packaging.

The invention is illustrated hereinafter by way of comparative examplesand invention examples. The percentages and ratios given in theseexamples are by weight unless otherwise indicated.

Subbing layer Nr. 01 on the emulsion side of the support:

copolymer of 88% vinylidene chloride, 10% 79.1 mg/m² methyl acrylate and2% itaconic acid Kieselsol ® 100F, a colloidal silica from BAYER 18.6mg/m² Mersolat ® H, a surfactant from BAYER  0.4 mg/m² Ultravon ® W, asurfactant from CIBA-GEIGY  1.9 mg/m²Ingredients used in the EXAMPLES:

-   POLYESTER:

MFI 270° C./ Inherent PET- 1.20 kg viscosity** T_(g) nr [cm³/10 min] [η][dl/g] [° C.] 01 T03* polyethylene 34.8 0.60 80.5 terephthalate 02 T04*polyethylene 34.8 0.60 80.5 terephthalate 03 WP75# polyester of 98.5 mol% 0.77 80 terephthalate, 1.5 mol % isophthalate and 100 mol % ethyleneunits 04 DP9990# polyester of 90 mol % 0.60 terephthalate, 10 mol %isophthalate and 100 mol % ethylene units 05 DP9970# polyester of 70 mol% terephthalate, 30 mol % isophthalate and 100 mol % ethylene units 06RADICRON polyester of 100 mol % 1480# terephthalate, 73 mol % ethyleneand 27 mol % neopentylene units 07 EASTAR copolyester of 100 mol % 77.7COPOLYESTER terephthalate, 64.2 mol % 6763## ethylene, 5.3 mol %ethyleneoxyethylene and 30.5 mol % cyclohexane- dimethylene### units 08EASTMAN copolyester of 100 mol % 72.5 COPOLYESTER terephthalate, 69.2mol % GP001## ethylene, 11.0 mol % ethyleneoxyethylene and 19.8 mol %cyclohexane- dimethylene### units *AGFA-GEVAERT N.V. ##EASTMAN ###ca.2:1 trans:cis #La Seda **inherent viscosity was determined in a 0.5 g/dLsolution of 60 wt % phenol and 40 wt % ortho-dichlorobenzene at 25° C.in an Ubbelohde viscometer

-   STYRENE-ACRYLONITRILE COPOLYMERS:

Wt % MFI at SAN- acrylo- Wt % 270° C./1.20 kg T_(g) nr nitrile styrene[mL/10 min] Mn Mw [° C.] 01 TYRIL 905* 20 80 7.1 105.2 02 TYRIL 867E* 2575 5.8 106.5 03 SAN 140* 27.5 72.5 53.2 47,640 99,820 108.8 04 LURAN368R# 28 72 3.9 107.3 05 TYRIL 790* 29 71 12.1 106.3 06 SAN 124* 28.571.5 37.9 53,940 109,350 108.1 07 LURAN 388S# 33 67 3.6 108.7 *DOWCHEMICAL #BASF MFI = Melt Flow Index

-   BARIUM SULPHATE: NEOBRK/renol white, a masterbatch from CLARIANT    GmbH containing 50% by weight barium sulphate and 50 wt % polyester-   TITANIUM DIOXIDE: Renol-white/PTX 506, a masterbatch from CLARIANT    GmbH containing 65% by weight TiO₂ and 35 wt % polyester

COMPARATIVE EXAMPLES 1 to 3

The PET-types and SAN-types used for producing the extrudates used inproducing of the films of COMPARATIVE EXAMPLES 1 to 3 are given inTable 1. The PET, SAN, TiO₂ and UVITEX OB-one in the weight percentagesgiven in Table 3 were mixed and then dried at 150° C. for 4 hours undervacuum (≦100 mbar), the mixtures then melted in a PET-extruder andextruded through a sheet die and cooled to produce the extrudates ofCOMPARATIVE EXAMPLES 1 to 3.

TABLE 1 Comparative PET01 PET02 PET03 SAN TiO₂ OB-one Example nr [wt %][wt %] [wt %] type [wt %] [ppm] C1 98 — — — 2 150 C2 47 — 47 — 6 — C3 44— 44 — 12 —The extrudates of COMPARATIVE EXAMPLES 1 to 3 were then longitudinallystretched with an INSTRON apparatus in which the extrudates are heatedin an oven mounted on the apparatus under the conditions given in Table2.

TABLE 2 Comparative Stretch Stretch force Thickness OD Example nr. ratio[N/mm²] [μm] TR924 C1/LS1 3.3 6.0 319 0.81 C2/LS1 3.3 5.0 340 1.26C3/LS1 3.3 5.0 65 1.59Transversal stretching was then performed on the longitudinallystretched films with a stretch time of 30 s and stretching speed of1000%/min under the conditions given in Table 3. Finally the films werethermally fixated at 175° C. for 1 minute giving the substantiallyopaque films of COMPARATIVE EXAMPLES 1/LS1, 2/LS2 and 3/LS3.

The optical densities of the films of COMPARATIVE EXAMPLES 1/LS1/BS1,2/LS1/BS1 and 3/LS1/BS1 were measured in transmission mode with aMACBETH TR924 densitometer with a visible filter and the results givenin Table 3.

TABLE 3 Stretch Comparative Stretch temperature Thickness OD (TR924)after Example nr. ratio [° C.] [μm] thermal fixation C1/LS1/BS1 3.3 135120 0.45 C2/LS1/BS1 3.3 135 140 0.90 C3/LS1/BS1 3.3 135 135 1.12 * thehigher the stretching tension the lower the stretch temperature

The films of COMPARATIVE EXAMPLES 1/LS/BS, 2/LS/BS and 3/LS/BS were eachmounted in an Instron 4411 apparatus and were heated at varioustemperatures between 120 and 190° C. for 5 seconds with a soldering ironin the upper clamp making contact with the film at a pressure of 0.5N/mm². The optical densities of the film after the tests were measuredin transmission with a MacBeth TR924 densitometer with a visible filterand the film thicknesses were also measured. The results are summarizedbelow in Tables 4 and 5 respectively.

TABLE 4 Film of OD OD after heating for 5 s at a % Comparative beforepressure of 0.5 N/mm² at ΔOD at reduction Example nr heating 120° C.130° C. 150° C. 170° C. 190° C. 150° C. in OD C1/LS/BS 0.45 0.47 0.460.46 0.47 0.45 −0.01 −0.01 C2/LS/BS 0.90 0.90 0.91 0.89 0.88 0.85 0.010.01 C3/LS/BS 1.12 1.14 1.14 1.11 1.11 1.08 0.01 0.01

TABLE 5 Layer Film of thickness Layer thickness after heating for 5 sComparative before at a pressure of 0.5 N/mm² at Example nr heating 120°C. 130° C. 150° C. 170° C. 190° C. C1/LS/BS 93 92 91 93 92 85 C2/LS/BS138 139 142 137 132 115 C3/LS/BS 137 136 135 139 131 119Within experimental error no transparentization was observed uponheating the films of COMPARATIVE EXAMPLES 1/LS/BS, 2/LS/BS and 3/LS/BS.This shows that in the absence of dispersed SAN-polymer particles thereis no transparentization of films containing titanium dioxide i.e. thereis no micro-void formation.

COMPARATIVE EXAMPLE 4

The 1083 μm thick extrudate of COMPARATIVE EXAMPLE 4 with a compositionof 2% by weight of titanium dioxide, 100 ppm UVITEX OB-one and 98% byweight of PET02 was produced as described for EXAMPLES 1 to 58 and hadan optical density measured with a MacBeth TR924 densitometer intransmission mode with a visible filter of 1.35. The extrudate wasstretched in the length direction as described in COMPARATIVE EXAMPLES 1to 3 under the conditions given in Table 6. The thickness values weremeasured by averaging measurements obtained by contacting the uppersurface at 16 different positions at a measuring force of 0.8N using aSONY U30A thickness gauge with a resolution of 1 μm, an accuracy of 2 μmand a contact ball 3 mm in diameter.

TABLE 6 Comparative Stretch Stretch force Thickness OD OD Example nr.ratio [N/mm²] [μm] (TR924) [X-rite] C4/LS1 3.3 6 323 0.805 0.55 C4/LS23.3 4 328 0.84 —Transversal stretching was then performed on the longitudinallystretched films with a stretch time of 30 s and stretching speed of1000%/min under the conditions given in Table 7. The measured thicknessand measured optical density with the MacBeth TR924 densitometer intransmission mode with a visible filter are also given in Table 7.

TABLE 7 Stretch Comparative Stretch temperature Thickness OD OD Examplenr. ratio [° C.] [μm] TR924 [X-rite] C4/LS1/BS1 3.3 135 120 0.47 0.30C4/LS2/BS1 3.3 135 124 0.53 0.6Since there is no contribution to the optical density from void-formingupon biaxial stretching for the composition of COMPARATIVE EXAMPLE 4 ascan be seen from COMPARATIVE EXAMPLE 1 to 3, the dependence of opticaldensity upon film thickness can be used to provide a baseline with whichto assess the contribution of void-forming to the optical density forthose compositions based upon aromatic polyesters with 2% by weight ofthe same titanium dioxide pigment which form voids upon biaxialstretching.

The Beer-Lambert relationship does not hold for pigmented films withlight-scattering pigments such as titanium dioxide. If the filmthickness is smaller than the average free path-length of the scatteredlight, light will escape after scattering otherwise the light does notescape and in fact interferes with further scattered light providing fora quasi-exponential dependence of optical density upon film thickness.The situation is too complex to be able to be described theoreticallyand hence the only possible approach is to measure the actual opticaldensity observed at particular film thicknesses. The above-mentionedoptical density appear to a fair approximation to bee linearly dependentupon the logarithm of the film thickness in the layer thickness range1084 to 120 μm giving the following relationship:

OD=0.891 log [thickness in μm]−1.3727

This relationship provides the optical density attributable to a 2% byweight concentration of the titanium dioxide pigment used as a functionof film thickness.

EXAMPLE 1 to 7

The ca. 1100 μm thick extrudates of EXAMPLES 1 to 7 all with 2% byweight of titanium dioxide and 15% by weight of SAN 06 were produced bymixing the ingredients in Table 8 in the proportions given in Table 8and then drying the mixture at 150° C. for 4 hours under vacuum (<100mbar) before melting in a PET-extruder, extrusion through a sheet dieand cooling to produce the extrudates of EXAMPLES 1 to 7 as summarizedin Table 8 together with the mole % of neopentylene units.

TABLE 8 Invention NP* PET02 PET06 SAN 06 UVITEX OB-one TiO₂ Example nr.[mol %] [% by wt] [% by wt] [% by wt] [ppm] [wt %] 1 5.2 66.3 16.7 15100 2.0 2 8.5 55.7 27.3 15 100 2.0 3 12.6 43.0 40.0 15 100 2.0 4 15.86.3 49.7 15 — 2.0 5 17.0 29.7 53.3 15 100 2.0 6 21.5 16.3 66.7 15 — 2.07 26.7 1.0 82.0 15 — 2.0 *NP = neopentylene units in polyesterStretching in the length direction was carried out for each extrudate asdescribed in COMPARATIVE EXAMPLES 1 to 3 under the conditions given inTable 9. The expected thickness is the thickness based on the extrudatethickness and longitudinal as observed for non-voided films.

TABLE 9 Longitudinal stretch Thickness OD Example force speedtemperature Density measured expected OD Expected ΔOD/ [X- nr. ratio[N/mm²] [m/min] [° C.] [g/mL] [μm] [μm] TR924 OD ΔOD OD rite] 1/BS1 3.39.55 4.0 387 333 0.84 2/BS1 3.3 9.55 4.0 366 333 0.82 3/BS1 3.3 8.27 4.0366 333 0.77 4/BS1 3.3 8.0 90 1.147 350 333 1.19 0.87 0.32 0.27 0.975/BS1 3.3 7.64 4.0 362 333 0.75 6/BS1 3.3 6.79 4.0 266 333 0.80 7/BS13.3 7.62 4.0 383 333 0.81 7/BS2 3.3 8.59 4.0 385 333 0.93Transversal stretching was then performed on the length-stretched filmwith a stretch time of 30 s and stretching speed of 1000%/min under theconditions given in Table 10. The measured thickness, the expectedthickness, i.e. thickness if no void-forming based on the extrudatethickness, the longitudinal stretch ratio and the transversal stretchratio, the measured optical density with the MacBeth TR924 densitometerin transmission mode with a visible filter, the expected optical densityand the difference between the observed optical density and the opticaldensity expected due to the aromatic polyester, ΔOD, are also given inTable 10.

TABLE 10 Stretch Expected OD Example Temperature Density Thicknessthickness OD Expected ΔOD/ [X- nr. ratio [° C.] [g/mL] [μm] [μm] TR924OD ΔOD OD rite] 1/LS1/BS1 3.5 100 1.17 141 95 0.81 2/LS1/BS1 3.5 95 1.07123 95 0.82 3/LS1/BS1 3.5 95 1.12 136 95 0.81 4/LS1/BS1 3.5 95 0.944 15095 1.28 0.89 0.39 0.69 1.02 5/LS1/BS1 3.5 95 1.12 133 95 0.85 6/LS1/BS13.5 100 1.03 135 95 0.87 7/LS1/BS1 3.5 100 0.96 139 95 0.83 7/LS2/BS13.5 100 147 95 0.98The results in Table 10 clearly show very substantial opacification, 69%of the optical density realized being due to void-forming with a matrixof a blend of PET and PETG.

The presence of void-forming was demonstrated for the biaxiallystretched films of INVENTION EXAMPLES 1/LS1/BS1, 2/LS1/BS2, 3/LS1/BS1,5/LS1/BS1 and 6/LS1/BS1 by clamping the films in an Instron 4411apparatus and observing the changes in film thickness and opticaldensity upon contacting the film with a soldering iron for 5 s atvarious temperatures. The results of these experiments are given inTable 11.

TABLE 11 Film after heating for 5 s at a pressure of 0.5 N/mm² thicknessat 150° C. at 170° C. Invention before OD Film Film thickness OD Exampleheating before thickness measured % % nr [μm] heating [μm] OD [μm] Δ μmdecrease measured Δ decrease 1/LS1/BS1 129 0.992 114 0.638 108.3 20.716.0 0.579 0.413 41.6 2/LS1/BS2 119 1.09 103 0.662 95.7 23.3 19.6 0.5510.539 49.4 3/LS1/BS1 134 1.1 106 0.582 101.7 32.3 24.1 0.510 0.59 53.65/LS1/BS1 121 1.07 102 0.608 88.7 32.3 26.7 0.537 0.533 49.8 6/LS1/BS1111 1.06 76 0.455 58 53 47.7 0.406 0.654 61.7A reduction in optical density at 170° C. varying from 0.413 for thefilm of INVENTION EXAMPLE 1/LS1/BS1 to 0.654 for the film of INVENTIONEXAMPLE 6/LS1/BS1 corresponding to 41.6 to 61.7%. These reductions inoptical density were accompanied by a reduction of 16 to 47.7% in layerthickness. These results show a large reduction in optical density of upto 0.654 upon transparentizing polyester layers with 15 wt % SAN 06 and2 wt % TiO₂.

EXAMPLE 8 to 13

The ca. 1100 μm thick extrudates of EXAMPLES 8 to 13 all with 2% byweight of titanium dioxide and 15% by weight of SAN 06 were produced bymixing the ingredients in Table 12 in the proportions given in Table 12and then drying the mixture at 150° C. for 4 hours under vacuum (<100mbar) before melting in a PET-extruder, extrusion through a sheet dieand cooling to produce the extrudates of EXAMPLES 8 to 13 as summarizedin Table 12.

TABLE 12 Invention mol % CHDM PET02 PET07 PET08 SAN 06 TiO₂ Exampleunits [% by wt] [% by wt] [% by wt] [% by wt] [wt %] 8 5.5 66.3 16.7 —15 2.0 9 11.3 49.6 33.4 — 15 2.0 10 17.4 33.0 50.0 — 15 2.0 11 5.5 58 —25 15 2.0 12 11.4 33 — 50 15 2.0 13 17.7 8 — 75 15 2.0 *CHDM =cyclohexanedimethylene units in polyesterStretching in the length direction was carried out for each extrudate asdescribed in COMPARATIVE EXAMPLES 1 to 3 under the conditions given inTable 13. The expected thickness is the thickness based on the extrudatethickness and longitudinal as observed for non-voided films.

TABLE 13 Longitudinal stretch stretching Thickness OD Example forcespeed temperature Density measured expected OD Expected [X- nr. ratio[N/mm²] [m/min] [° C.] [g/mL] [μm] [μm] TR924 OD rite]  8/LS1 3.3 9.24.0 89 1.25 358 333 1.26 0.87 0.92  8/LS2 3.3 4.0 75 1.21 347 333 1.230.87 0.95  9/LS1 3.3 7.9 4.0 89 1.25 347 333 1.21 0.87 0.89  9/LS2 3.34.0 75 1.20 371 333 1.33 0.87 1.0 10/LS1 3.3 6.9 4.0 90 1.24 338 3331.67 0.87 1.34 10/LS2 3.3 4.0 72 333 1.09 0.87 0.85 11/LS1 3.3 8.8 4.091 1.24 359 333 1.21 0.87 0.95 11/LS2 3.3 4.0 75 1.19 379 333 1.37 0.871.05 12/LS1 3.3 6.7 4.0 91 333 0.87 13/LS1 3.3 4.2 4.0 90 333 0.8713/LS2 3.3 4.0 74 333 0.87Transversal stretching was then performed on the length-stretched filmwith a stretch time of 30 s and stretching speed of 1000%/min under theconditions given in Table 14. The measured thickness, the expectedthickness, i.e. thickness if no void-forming based on the extrudatethickness, the longitudinal stretch ratio and the transversal stretchratio, the measured optical density with the MacBeth TR924 densitometerin transmission mode with a visible filter, the expected optical densityand the difference between the observed optical density and the opticaldensity expected due to the aromatic polyester, ΔOD, and the opacitydetermined using a Hunterlab apparatus according to ASTM D589 C/2° arealso given in Table 14.

TABLE 14 opacity Stretch Expected OD ASTM Invention Temperature DensityThickness thickness OD Expected ΔOD/ [X- D589 example nr ratio [° C.][g/mL] [μm] [μm] TR924 OD ΔOD OD rite] C/2°  8/LS1/BS1 3.5 100 1.13 13095 1.04 0.89 0.15 0.14 0.85 93.8  8/LS1/BS2 3.5 90 1.07 148 95 1.12 0.890.23 0.20 0.88 94.7  8/LS2/BS1 3.5 100 1.02 170 95 1.13 0.89 0.24 0.210.96 95.8  8/LS2/BS2 3.5 90 1.09 177 95 1.17 0.89 0.28 0.24 0.97 95.2 9/LS1/BS1 3.5 100 1.12 131 95 1.01 0.89 0.12 0.12 0.84 93.1  9/LS1/BS23.5 90 1.09 160 95 1.07 0.89 0.18 0.17 0.86 94.3  9/LS2/BS1 3.5 100 1.05142 95 1.21 0.89 0.32 0.26 0.99 95.3  9/LS2/BS2 3.5 90 1.04 174 95 1.240.89 0.35 0.28 1.02 96.4 10/LS1/BS1 3.5 100 1.08 149 95 1.08 0.89 0.190.18 0.86 94.4 11/LS1/BS1 3.5 100 1.01 144 95 1.14 0.89 0.25 0.22 0.9195 11/LS1/BS2 3.5 90 1.01 167 95 1.17 0.89 0.28 0.24 0.96 95.711/LS2/BS1 3.5 90 0.93 168 95 1.28 0.89 0.39 0.30 1.07 96.8 12/LS1/BS13.5 100 1.00 153 95 1.21 0.89 0.32 0.26 1.02 96.2 12/LS1/BS2 3.5 90 0.96177 95 1.23 0.89 0.34 0.28 1.08 97 13/LS1/BS1 3.5 100 1.28 164 95 1.000.89 0.11 0.11 0.86 94.1 13/LS1/BS2 3.5 90 1.04 136 95 1.08 0.89 0.190.18 0.82 93.1 13/LS2/BS1 3.5 100 1.02 144 95 1.10 0.89 0.21 0.19 1.0096.2The results in Table 14 clearly show very substantial opacification, theopacity measurements roughly correlating with the optical densitymeasurements obtained with the X-rite desistometer.The present invention may include any feature or combination of featuresdisclosed herein either implicitly or explicitly or any generalisationthereof irrespective of whether it relates to the presently claimedinvention. In view of the foregoing description it will be evident to aperson skilled in the art that various modifications may be made withinthe scope of the invention.

Having described in detail preferred embodiments of the currentinvention, it will now be apparent to those skilled in the art thatnumerous modifications can be made therein without departing from thescope of the invention as defined in the following claims.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

Preferred embodiments of this invention are described herein, includingthe best mode known to the inventors for carrying out the invention. Ofcourse, variations of those preferred embodiments will become apparentto those of ordinary skill in the art upon reading the foregoingdescription. The inventors expect skilled artisans to employ suchvariations as appropriate, and the inventors intend for the invention tobe practiced otherwise than as specifically described herein.Accordingly, this invention includes all modifications and equivalentsof the subject matter recited in the claims appended hereto as permittedby applicable law. Moreover, any combination of the above-describedelements in all possible variations thereof is encompassed by theinvention unless otherwise indicated herein or otherwise clearlycontradicted by context.

1. A film consisting essentially of a continuous phase linear polyestermatrix having dispersed therein a non-crosslinked random SAN-polymer anddispersed or dissolved therein at least one ingredient from the group ofingredients consisting of inorganic opacifying pigments, whiteningagents, colorants, UV-absorbers, light stabilizers, antioxidants andflame retardants, wherein said film is white, microvoided,non-transparent and axially stretched; said linear polyester matrix hasmonomer units consisting essentially of at least one aromaticdicarboxylic acid, at least one aliphatic diol and optionally at leastone aliphatic dicarboxylic acid; the weight ratio of said linearpolyester to said non-crosslinked SAN-polymer is in the range of 2.0:1to 19.0:1; and one of the said at least one aliphatic dimethylenemonomer units is selected from the group consisting of neopentylene and1,4-cyclohexanedimethylene in a concentration of 30 mole % or less ofall aliphatic dimethylene monomer units.
 2. The film according to claim1, wherein said film is a biaxially stretched film.
 3. The filmaccording to claim 1, wherein the concentration of inorganic opacifyingpigment is ≧0.1% by weight.
 4. The film according to claim 1, whereinone of the said at least one aliphatic dimethylene monomer units isselected from the group consisting of neopentylene and1,4-cyclohexanedimethylene in a concentration of 20 mole % or less ofall aliphatic dimethylene monomer units,
 5. The film according to claim1, wherein the concentration of AN-monomer units in said SAN-polymer is15 to 35% by weight.
 6. The film according to claim 1, wherein saidweight ratio of said linear polyester to said non-crosslinkedSAN-polymer is in the range 2.7:1 to 9.0:1.
 7. A process for using insynthetic paper a film consisting essentially of a continuous phaselinear polyester matrix having dispersed therein a non-crosslinkedrandom SAN-polymer and dispersed or dissolved therein at least oneingredient from the group of ingredients consisting of inorganicopacifying pigments, whitening agents, colorants, UV-absorbers, lightstabilizers, antioxidants and flame retardants, wherein said film iswhite, microvoided, non-transparent and axially stretched; said linearpolyester matrix has monomer units consisting essentially of at leastone aromatic dicarboxylic acid, at least one aliphatic diol andoptionally at least one aliphatic dicarboxylic acid; the weight ratio ofsaid linear polyester to said non-crosslinked SAN-polymer is in therange of 2.0:1 to 19.0:1; and one of the said at least one aliphaticdimethylene monomer units is selected from the group consisting ofneopentylene and 1,4-cyclohexanedimethylene in a concentration of 30mole % or less of all aliphatic dimethylene monomer units.
 8. An imagerecording element comprising a film consisting essentially of acontinuous phase linear polyester matrix having dispersed therein anon-crosslinked random SAN-polymer and dispersed or dissolved therein atleast one ingredient from the group of ingredients consisting ofinorganic opacifying pigments, whitening agents, colorants,UV-absorbers, light stabilizers, antioxidants and flame retardants,wherein said film is white, microvoided, non-transparent and axiallystretched; said linear polyester matrix has monomer units consistingessentially of at least one aromatic dicarboxylic acid, at least onealiphatic diol and optionally at least one aliphatic dicarboxylic acid;the weight ratio of said linear polyester to said non-crosslinkedSAN-polymer is in the range of 2.0:1 to 19.0:1; and one of the said atleast one aliphatic dimethylene monomer units is selected from the groupconsisting of neopentylene and 1,4-cyclohexanedimethylene in aconcentration of 30 mole % or less of all aliphatic dimethylene monomerunits.
 9. The image recording element according to claim 8, wherein saidimage is a non-photographic image.
 10. The image recording elementaccording to claim 8, wherein said film is provided on at least one sidewith an overprintable layer.
 11. The image recording element accordingto claim 8, wherein said film is provided on at least one side with anon-transparent transparentizable overprintable layer.
 12. The imagerecording element according to claim 8, wherein said film is provided onat least one side with an ink-jet receiving layer.
 13. The imagerecording element according to claim 8, wherein said film is provided onat least one side with an imaging layer.
 14. The image recording elementaccording to claim 8, wherein said film is provided with a writablelayer.
 15. A process for preparing a non-transparent microvoided axiallystretched film comprising the steps of: i) mixing at least one linearpolyester having monomer components consisting essentially of at leastone aromatic dicarboxylic acid, at least one aliphatic diol andoptionally at least one aliphatic dicarboxylic acid, a non-crosslinkedrandom SAN-polymer and at least one ingredient from the group ofingredients consisting of inorganic opacifying pigments, whiteningagents, colorants, UV-absorbers, light stabilizers, antioxidants andflame retardants in a kneader or an extruder to produce a mixturecomprising said non-crosslinked random SAN-polymer in a polyestermatrix, ii) forming the mixture produced in step i) in a thick filmfollowed by quenching; and iii) stretching said thick film at astretching tension of >2.5 N/mm² at a temperature between the glasstransition temperature of said SAN-polymer and the glass transitiontemperature of said linear polyester to at least twice the initiallength, wherein the weight ratio of said polyester matrix to saidnon-crosslinked random SAN-polymer is in the range of 2.0:1 to 19.0:1and wherein one of the said at least one aliphatic dimethylene monomerunits is selected from the group consisting of neopentylene and1,4-cyclohexanedimethylene in a concentration of 30 mole % or less ofall aliphatic dimethylene monomer units.
 16. The process according toclaim 15, wherein said process comprises a further step, step (iv) inwhich said film is subjected to a further stretching process at an anglesubstantially 90° to the first stretching process to at least twice theinitial length at a stretching tension of >2.5 N/mm² and a temperaturebetween the glass transition temperature of said SAN-polymer and theglass transition temperature of the linear polyester
 17. The processaccording to claim 15, wherein step iv) is performed at a filmtemperature at or below 120° C.
 18. The process according to claim 15,wherein steps iii) and iv) are performed simultaneously.
 19. The processaccording to claim 15, wherein at least one of said at least onearomatic dicarboxylic acid monomer units is isophthalic acid and saidisophthalic acid is present in said polyester matrix in a concentrationof 15 mole % or less of all the dicarboxylic acid monomer units in saidlinear polyester matrix.
 20. A process for obtaining a transparentpattern comprising the step of: image-wise application of heatoptionally supplemented by the application of pressure to a filmconsisting essentially of a continuous phase linear polyester matrixhaving dispersed therein a non-crosslinked random SAN-polymer anddispersed or dissolved therein at least one ingredient from the group ofingredients consisting of inorganic opacifying pigments, whiteningagents, colorants, UV-absorbers, light stabilizers, antioxidants andflame retardants, wherein said film is white, microvoided,non-transparent and axially stretched; said linear polyester matrix hasmonomer units consisting essentially of at least one aromaticdicarboxylic acid, at least one aliphatic diol and optionally at leastone aliphatic dicarboxylic acid; the weight ratio of said linearpolyester to said non-crosslinked SAN-polymer is in the range of 2.0:1to 19.0:1; and one of the said at least one aliphatic dimethylenemonomer units is selected from the group consisting of neopentylene and1,4-cyclohexanedimethylene in a concentration of 30 mole % or less ofall aliphatic dimethylene monomer units.